Unitary locking cap for use with a pedicle screw

Abstract

A unitary locking cap mechanism, which is used with pedicle screws and other orthopaedic implant devices which couple bones to rods, includes rim and post portions which are rotationally freely coupled to one another to permit independent motion relative to one another. The rim element has a cylindrical body with an open end and a closed end; the closed end alternatively having a concentric hole defined by an inwardly directed flange. In one embodiment, the flange includes a series of slots, dividing into a plurality of wedge-shaped pie sections. In another embodiment, the sidewall of the cylindrical portion of the rim includes an annular recess. The post is a cylindrical shaft having surface elements at one end which provide for mutual engagement with the rim. These surface elements may be deflecting arms which seat into the annular recess of the rim, or an annular recess in the shaft into which the wedge-shaped pie sections of the flange portion may be resiliently snapped into. In an alternative embodiment, the shaft and the rim are coupled together through the concentric hole by a retaining ring which is placed around the shaft, in an annular recess therein, after the insertion of the shaft through the hole. Each embodiment are alternatively designed such that the post or the inner surface of the rim portions are threaded so that it can mate with a threading on the inner or outer upwardly extending, U-shaped channel forming, members of the heads of the pedicle screws.

We claim: 
     
       1. A unitary locking cap for locking a rod in a rod receiving channel defined between a pair of upwardly extending members of an orthopaedic implant apparatus, said upwardly extending members each having mutually defined exterior and interior surfaces a threading on one of said exterior and interior surfaces, comprising: a cylindrical body having a sidewall having inner and outer surfaces, said inner surface including an annular recess, a first end, which is open, and a second end, said body being mountable around the mutually defined exterior surfaces of said pair of upwardly extending members;   a post member which is positionable between said mutually defined interior surfaces of said pair of upwardly extending members, said post member including a plurality of deflecting arms extending radially therefrom which seat in the annular recess of said cylindrical body such that the post and the cylindrical body may rotate independently, but such that the post may not be removed;   a corresponding threading for engaging the threading on the upwardly extending members.   
     
     
       2. The assembly as set forth in claim 1, wherein said threading on said upwardly extending members is provided on exterior surfaces thereof and wherein said corresponding threading for engaging this threading on the exterior surfaces of the upwardly extending members is provided on the inner surface of said cylindrical body. 
     
     
       3. The assembly as set forth in claim 1, wherein said threading on said upwardly extending members is provided on interior surfaces thereof and wherein said corresponding threading for engaging this threading on the interior surfaces of the upwardly extending members is provided on the post. 
     
     
       4. A unitary locking cap for locking a rod in a rod receiving channel defined between a pair of upwardly extending members of an orthopaedic implant apparatus, said upwardly extending members each having mutually defined exterior and interior surfaces a threading on one of said exterior and interior surfaces, comprising: a cylindrical body having a sidewall having inner and outer surfaces, a first end, which is open, and a second end, said second end including an inwardly directed flange which comprises a plurality of radial slots therein dividing the flange into wedge-shaped sections, said flange defining a hole having a first diameter, said body being mountable around the mutually defined exterior surfaces of said pair of upwardly extending members;   a post member having a second diameter which is greater than the first diameter and at least one annular recess having a third diameter which is less than the first diameter such that the post is axially positionable in said hole by inserting the post therethrough, causing the deflection of the inwardly directed slotted flange until the inwardly directed slotted flange seats in the annular recess of the post, thereby permitting the post and cylindrical body may rotate independently while the post is axially retained in the hole; and   a corresponding threading for engaging the threading on the upwardly extending members.   
     
     
       5. The assembly as set forth in claim 4, wherein said sidewall of said cylindrical body has a reduced thickness at a circumferential junction of said inwardly directed flange such that said wedge-shaped sections may deflect resiliently. 
     
     
       6. An orthopaedic rod implant apparatus, comprising: at least one rod;   at least one corresponding bone-to-rod coupling device having a head, said head including a pair of upwardly extending members defining therebetween a rod receiving channel, said upwardly extending members each having mutually defined exterior and interior surfaces a threading on one of said exterior and interior surfaces; and   a unitary locking cap for securely locking said rod in said channel of said head of said bone-to-rod coupling device, said cap being mountable around the mutually defined exterior surfaces of said upwardly extending members, said cap including   a cylindrical body having a sidewall having inner and outer surfaces, said inner surface including an annular recess, a first end, which is open, and a second end, said body being mountable around the mutually defined exterior surfaces of said pair of upwardly extending members;   a post member which is positionable between said mutually defined interior surfaces of said pair of upwardly extending members, said post member including a plurality of deflecting arms extending radially therefrom which seat in the annular recess of said cylindrical body such that the post and the cylindrical body may rotate independently, but such that the post may not be removed;   a corresponding threading for engaging the threading on the upwardly extending members.   
     
     
       7. An orthopaedic rod implant apparatus, comprising: at least one rod;   at least one corresponding bone-to-rod coupling device having a head, said head including a pair of upwardly extending members defining therebetween a rod receiving channel, said upwardly extending members each having mutually defined exterior and interior surfaces a threading on one of said exterior and interior surfaces; and   a unitary locking cap for securely locking said rod in said channel of said head of said bone-to-rod coupling device, said cap being mountable around the mutually defined exterior surfaces of said upwardly extending members, said cap including a cylindrical body having a sidewall having inner and outer surfaces, a first end, which is open, and a second end, said second end including an inwardly directed flange which comprises a plurality of radial slots therein dividing the flange into wedge-shaped sections, said flange defining a hole having a first diameter, said body being mountable around the mutually defined exterior surfaces of said pair of upwardly extending members;   a post member having a second diameter which is greater than the first diameter and at least one annular recess having a third diameter which is less than the first diameter such that the post is axially positionable in said hole by inserting the post therethrough, causing the deflection of the inwardly directed slotted flange until the inwardly directed slotted flange seats in the annular recess of the post, thereby permitting the post and cylindrical body may rotate independently while the post is axially retained in the hole; and   a corresponding threading for engaging the threading on the upwardly extending members.   
     
     
       8. The assembly as set forth in claim 7, wherein said sidewall of said cylindrical body has a reduced thickness at a circumferential junction of said inwardly directed flange such that said wedge-shaped sections may deflect resiliently.